The present invention relates to an apparatus for conducting electrolytic reactions in an aqueous phase and more particularly for reducing plutonium and/or uranium contained in an aqueous phase by means of electrolysis, the reduction taking place between electrodes connected to a current source.
During reprocessing of nuclear fuels there develops, among other things, a nitric acid solution of plutonium and uranium. Generally, it is desirable to concentrate or enrich this solution and separate the plutonium in it from the uranium. Thus, the nitric acid-plutonium-uranium solution is initially concentrated to a small volume for reasons of economy and in this concentrated solution the plutonium is electrolytically reduced to plutonium (III) and then separated by precipitation as plutonium (III) oxalate. The precipitation and electrolysis should be conducted in a concentration of free nitric acid which is as high as possible. Small quantities of residual uranium, however, are tolerable.
It is known to electrolytically reduce plutonium (IV) -- uranium (VI) solution in 1 molar nitric acid (British Patent No. 1,096,592). The prior art, however, has not taught that a plutonium (IV)/(III) reduction can be successfully accomplished in strong nitric acid. Moreover, persons skilled in the art doubt that plutonium (III) is stable in strong nitric acid. Thus, 3mHNO.sub.3 has been considered to be the upper tolerance limit for the stability of plutonium (III) in an aqueous solution from which the plutonium is to be precipitated.
Accordingly, it is a primary object of the present invention to develop an apparatus which is suitable for commercial operation and which permits a quantitative plutonium (IV)/(III) reduction to be effected continuously in a single stage. As used in this specification and claims, the term "in a single stage" indicates that the plutonium (IV)/(III) reduction is quantitative in a single electrolysis cell (stage). It is another object of this invention to provide an apparatus and method wherein the plutonium (III) in the reduced solution is stable to permit its separation by precipitation from the aqueous solution. A further object of this invention is to provide an electrolysis cell having a reduction electrode that has a large area, but which is not oversized and can be conveniently used in normal application.